Compared to the 1990's Moore's law stopped really making CPUs faster around 10 years ago. We now have more cores, but getting performance gains from parallelism can be hard.

I think the real reason software may be more buggy is that good quality software takes too long to develop. There is a big commercial advantage in being first to market.

Constant updates over the web also mean that you don't need to test so much before shipping. You can always send a patch later. This was different when software was shipped on disks.